This invention relates to hydraulic control valves and more particularly to sliding spool type control valves provided with a detent mechanism.
Control valves of the type contemplated include a valve body having an elongated bore in which a reciprocally actuated spool is movable from a neutral position to a detented position for controlling fluid flow through passages formed in the valve body. The spool is engaged by a centering spring which in the absence of other forces acting on the spool urges the spool to the neutral position. In the detented position, a detent mechanism applies a detenting force to the spool which holds or locks movement of the spool against the biasing force of the centering spring.
In a known type of mechanical detent the centering spring and the detent mechanism are housed in an end cap detachably mounted to the valve body. The detent mechanism includes a spool extension having one or more detent grooves formed therein and is attached to the valve spool for movement therewith. The spool extension is mounted for sliding movement in a stationary ball retainer positioned in the end cap. The ball retainer mounts a plurality of balls for radial movement in an axially aligned row with the balls spaced radially around the periphery of the spool extension. A movable ring-shaped clapper member rides on the row of balls and a detent spring acting on the clapper provides a detenting force that urges the balls radially against the periphery of the spool extension. Both the biasing force and the detenting force combine to form a shifting force required to move the spool from the neutral position to the detented position.
Movement of the spool from the neutral position aligns a detent groove with the row of balls. As the groove is aligned with the row of balls the detenting force drives the balls radially into the groove. In this position, the resulting force balance between the biasing force and the detenting force securely locks the spool against the biasing force tending to return the spool to the neutral position. Release of the spool from the detented position requires displacement of the clapper member effecting a change in the force balance wherein the biasing force acting on the balls through the detent groove drives the balls radially outward of the detent groove to free the spool extension and spool for return to the neutral position.
Control valves of the type described control equipment used for earth moving, construction, and mining applications. These applications require increasingly powerful force multiplying actuators resulting in increased fluid pressure acting on the valve spools. The increased pressure calls for stronger centering and detent spring forces with a corresponding increase in the shifting forces required to move the spool. In lever actuated spools, the increased shifting force leads to operator fatigue after repeated actuations.
The present invention is directed to providing a magnetic detent mechanism for reducing the shifting force required to move the spool of a control valve during movement of the spool to a detented position.
To this end a magnetic detent mechanism is provided for a control valve having a sliding spool movable from a neutral position to a detented position. The magnetic detent is housed within an end cap detachably mounted to the valve. The magnetic detent includes a movable spool extension attached to the spool for movement therewith and having a detent groove formed therein. A stationary ball retainer mounted in the end cap includes a bore extending therethrough supporting the spool extension for sliding movement therein. A plurality of balls are mounted in the ball retainer and held thereby for radial movement and in contact with the periphery of the spool extension. A centering spring mounted in the cap between the ball retainer and the valve imparts a biasing force to the spool urging the spool and attached spool extension from the detented position to the neutral position. A magnet member having a predetermined magnetic force is mounted in the end cap spaced from the centering spring on the opposite side of the ball retainer. A clapper member having an inclined ramp portion riding on the balls is movable between the ball retainer and the magnet member. A spring member engaging the clapper member exerts a pre-load force on the clapper member urging the clapper member into contact with the magnet member and urging the balls radially for engagement with the detent groove.
With the spool moved to the detented position the balls are driven into the detent groove by the pre-load force acting on the clapper member. The pre-load force also drives the clapper member into contact with the magnet member. The clapper member is held by the magnetic force which combines with the pre-load force to form a detenting force acting on the balls which are engaged in the detent groove. The resulting force balance between the detenting force and the biasing force locks the spool against the biasing force tending to return the spool to the neutral position. Inasmuch as the spool extension senses the effects of the detenting force only after the balls are engaged in the detent groove, the shifting force required to move the spool to the detented position need only be sufficient to overcome the combined biasing and pre-load forces acting on the spool extension.
Further advantages and details of my invention can be had from the following description and claims taken together with the accompanying drawing.